Nickel-iron base magnetic material with high initial permeability at low temperatures

ABSTRACT

A nickel-iron base alloy is described to which controlled amounts of copper, manganese and molybdenum may be added. By proper selection of composition and heat treatment high initial permeabilities are obtained at cryogenic temperatures.

nited States Patent 7 1151 3,07,02

Pieifer [4 1 Apr. 1, 1972 1541 NICKEL-IRON BASE MAGNETIC MATERIAL WITHHIGH INITIAL 1 Ref r nces Cited LOW UNITED STATES PATENTS 3,546,03112/1970 Pfeifer et a1. ..l48/121 [72] Inventor: Friedrich Pfeifer,Oberissigheim, Kreis, 3,556,876 1/1971 Pfeifer et all ..148/ 121 Hanau,Germany 1,552,769 911925 Smith et a1 .75/170 1,768,443 6 1930 Elmen..75/170 [731 Asslgnee= Vacuumschme' Hana, Germany 3,269,834 8/1966Lykensetal ..75/170 22 Filed: Mar. 17, 1969 3,472,708 10/196956161161616161. .75/170 [2 App 8071652 Primary Examiner-Richard 0. DeanAttorney-F. Shapoe and R. T. Randig Foreign Application Priority Data57] ABSTRACT 1968 Germany 58 152'l A nickel-iron base alloy is describedto which controlled amounts of copper, manganese and molybdenum may be52 us. (:1 ..148/31.55, /170, 148/120, added By proper Selectionofcomposition and heat treatment I t Cl high initial permeabilities areobtained at cryogenic temperan tu [58] Field 618661611..75/l70;l48/31.55,3l.57,100,- res 148/104, 120, 121 6 Claims, 9 DrawingFigures 10 COMMERCIAL 9 Ni-Fe-Mo ALLOY I I '5 520C E5 Lu 2 1: 11.1 o.

I i ALLOY 3 Z -20o 0 TEMPERATURE (C) PATENTED PR 18 m2 SHEET 10F 2PATENTEDAPR 18 m2 SHEET 2 BF 2 O U. o.

ALLOY 9 ALLOY a -2bo -|c' o c' TEMPERATURE (c) FIG. 5.

NICKEL-IRON BASE MAGNETIC MATERIAL WITH HIGH INITIAL PERMEABILITY AT LOWTEMPERATURES BACKGROUND OF THE INVENTION current instrument transformersand transmitters which operate at cryogenic temperatures such asobtained in liquid nitrogen or helium. For this type of application, themagnetically soft material must have as high as possible an initialpermeability in the range of low temperatures. In magnetic shielding,the high initial permeability is a desirable condition for highlyeffective shielding against extremely weak extraneous magnetic fields.Moreover, for the current transformers, the indication or measuringerror becomes smaller with increasing permeability of the transformermaterial, while in case of low current transmitters a very highinductivity can be obtained with a small number of turns if thetransmitter material has a high permeability at small field intensities.

The high permeability magnetically soft materials which have beenheretofore known have not met the above stated requirements. Therelative permeability of the magnetically softest alloys with 70 to 80%of nickel when measured at room temperature and at a field intensity of0.5 mOe (millioersted) is over 100,000 and decreases sharply with lowertemperatures to about 10,000 to 15,000 at a temperature of -1 20 C.

In comparison, sendust alloys, that is, the ternary iron base alloyswith about 7 to 14% of silicon and with about 2 to 7% of aluminum andwhich also fall into this category of the technology, reach higherpermeability values even slightly below C. but these higher permeabilityvalues are achieved in a relatively narrow range of temperature andthese values are obtained only for field intensities of about 40 to 200mOe, that is, for relatively high field intensities. Moreover, the pointof maximum permeability depends specifically on the respective siliconand aluminum content of the alloy. For example, an iron-silicon-aluminumalloy with 9.9% of silicon and 5.6% of aluminum has at 1 00 C. a sharplydefined maximum with a peak value of permeability of about 64,000 at afield intensity of 100 mOe. For field intensities below 30 mOe thepermeability decreases to less than 15,000; moreover, for a fieldintensity of 1 mOe, the permeability amounts to even less than 10,000(see Journal of Physics, 1941, vol. IV, pages 569 to 572).

More importantly however the iron-silicon-aluminum alloys of the abovespecified composition are not suitable for many applications not only onthe basis of their unfavorable dependency of their permeability on thefield intensity but also because of their technological characteristics,that is, their high degree of brittleness (see C. Heck: MagneticMaterials and Their Technical Applications, 1967, pages 403 and 404)does not permit any of the usual forming or cutting operations (otherthan grinding) and correspondingly there cannot be produced from thesematerials any strips, core laminations, or deep-drawn parts.

SUMMARY OF THE INVENTION Therefore the purpose of this invention is toobtain in ductile alloys the best possible magnetically soft propertiesat low temperatures. The invention is based specifically on the problemof preparing a nickel-iron base magnetic material which has, attemperatures below 180 C., a relative initial permeability of more than40,000 in weak magnetic fields.

Broadly speaking this is accomplished by selecting the alloyingcomponents such that there is present between about 8.9% and 27.6% iron,up to 12.5% copper, up to 4.6% molybdenum, from about 0.2% to about 1.0%manganese and the balance essentially nickel with incidental impurities.The alloy is thereafter processed by hot and cold working and the finishgauge material is thereafter annealed at a temperature within the rangebetween about 1,050" and about l250 C. for a time period of betweenabout 2 hours, and, about 8 hours followed by cooling to roomtemperature. The annealed material is then subjected to a final heattreatment at a temperature between the Curie temperature and 550 C. fora time period of between about 1 hour and about 5 hours followed byquenching to room temperature.

An object of the present invention is to provide a ductile nickel-ironbase alloy having high initial permeability at cryogenic temperaturesand at low field intensities.

A specific object of the present invention is to provide a ductilenickel-iron base magnetic material and a heat treatment therefor wherebythe material will exhibit an initial permeability of at least 40,000 ina field intensity of 0.5 mOe at a temperature of less than 180 C.

Other objects of the present invention will become apparent to thoseskilled in the art when read in conjunction with the followingdescription and the drawings in which:

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a ternary diagram illustratingthe broad and preferred limits of the alloying components;

FIG. 2 is a ternary diagram illustrating the relation of the coppercontent with respect to the balance of the alloying components;

FIG. 3 is similar to FIG. 1 but illustrating the actual composition ofalloys made and tested as set forth in Table I; and

FIGS. 4 through 9 inclusive illustrate the relationship between initialpermeability and temperature for alloys 3, 8, l9, l5, 9 and 17respectively of Table I.

DESCRIPTION OF PREFERRED EMBODIMENT The alloy of the present inventionis a nickel-iron base alloy to which controlled amounts of at least oneof copper, manganese and molybdenum are added. While in broad generalterms the alloy contains, in percent by weight, from about 8.9% to about27.6% iron, up to 12.5% copper, up to 4.6% molybdenum, from about 0.2%to about 1.0% manganese and the balance nickel incidental impurities,the alloying components must be balanced in accordance with thecircumscribed areas of FIGS. 1 and 2.

More particularly, according to this invention the actual composition ofthe magnetic material lies within or in immediate vicinity of a range ofmulticomponent system nickel- (iron copper manganese)-molybdenum whichis defined in FIG. 1 by the polygon A (73.3% Ni; 26.7% (Fe+Cu+Mn); 0%Mo)- B (80.5% Ni; 16.9% (Fe+Cu+Mn); 2.6% Mo) C (80.5% Ni; 14.9%(Fe+Cu+Mn); 4.6% Mo) D (72.2% Ni; 26.3% (Fe+Cu+Mn); 1.5% Mo) E (72.2%Ni; 27.8% (Fe+Cu+Mn); 0% Mo)-A.

The preferred range of alloying components is defined by the polygon F(75.4% Ni; 23.2% (Fe+Cu+Mn); 1.4% Mo) G (78.0% Ni; 19.7% (Fe+Cu+Mn);2.3% Mo) H (78.0% Ni; 18.5% (Fe+Cu+Mn); 3.5% Mo) J (75.4% Ni; 22.1%(Fe+Cu+Mn); 2.5% Mo)-F with the restriction that the content ofmanganese is 0.2 to 1.0% in each instance. Moreover, the content ofcopper associated with the content of nickel must be within the rangewhich in FIG. 2 is determined by the polygon K (72.2% Ni; 19.4%(Fe-l-Mn-l-Mo); 8.4% Cu) L (77.5% Ni; 22.5% (Fe+Mn-l-Mo); 0% Cu) M(80.5% Ni; 19.5% (Fe+Mn-l-Mo); 0% Cu) N (80.5% Ni; 18.1% (Fe-l-Mni-Mo);1.4% Cu) O (73.0% Ni; 14.5% (Fe+Mn+Mo); 12.5% Cu) P (72.2% Ni; 15.3%(Fe+Mn+Mo); 12.5% Cu)-K. Preferred results are obtained where the coppercontent is maintained within the polygon O (75.4% Ni; 21.3% (Fe+Mn+Mo);3.3% Cu) R (78.0% Ni; 18.7% (Fe+Mn+Mo); 3.3% Cu) S (78.0% Ni; 17.0%(Fe+Mn+Mo); 5.0% Cu) T (75.4% Ni; 19. 6% (Fe+Mn+Mo); 5.0% Cu)-Qof FIG.2.

When the alloying components are balanced within the circumscribed areasof FIGS. 1 and 2, the material is annealed during its manufacture in anon-oxidizing atmosphere for several hours, specifically 2 to 8 hours,at 1,050 to 1,250 C. and afterwards it is subjected to final heattreatment for several hours, specifically l to hours, at a temperaturein a vacuum fumace there were produced nickel-iron alloys with thechemical composition given in per cent by weight in Table l andindicated by the same numbers in the nickel- (iron coppermanganese)-molybdenum alloying diagram in FIG. 3. After forging, theingots were hot rolled to a thickness of 2.5 mm followed by annealing atl,050 C. Thereafter, the material was cold rolled to a final thicknessof 0.1 mm with intermediate annealing where necessary. From the strip0.1 mm thick and 10 mm wide there were produced wound ring cores of mminside diameter and mm outside diameter. These cores were then annealedfor 5 hours at 1,200 C. in pure hydrogen, cooled to room temperature,subjected to final heat treatment in hydrogen at the time andtemperatures set forth in Table I1 and subsequently the cores were 0between the Cum temperatur? and 550 15 quickly brought to roomtemperature.

Improvement of the magnetic propertles in the range of low 1temperatures obtained by the selection of alloying and heat The P P Y (l-0.5) ofthe f cores was determined y treatment canbeseen from thefollowing examples. Reference a Maxwell budge at field lmellsflty of mos0 at the is directed to Table I and to FIG. 3 which tabulates the chemiffl of t These condnlms closely approxlmate the cal composition of anumber of alloys which were made and 20 i f For measuring dependency ofthe meet pen'neabllity of the temperatures in the range between 268.9 C.and +20 C., the cores were placed in a suitable TABLE I protectivecopper casing, cooled in a cryostat to the tempera- [Chemlcal composmoby Weghm ture of liquid helium (i.e. 268.9 C.) or liquid nitrogen (i.e.Ni Fe Cu Mo Mn Si 25 195.8 C.) and then permitted to warm naturallywhile the 75. 00 20 L 63 Trace permeability and temperatures were monitored. The measure- 70.05 17.25 4. 37 1.75 0.50 0.02 ments of thetemperatures below 200 C. were made by g" g" 8} means of agoldiron-chromel thermocouple and above -200 77. 50 15. 30 4. 5g 2. 238. 01 T 3 3 C. by means of a copper-constantan thermocouple which was77. 05 14. 30 4. 4 2. 32 .03 70.35 10. 50 4.75 1.50 8.03 0. 0 30 P a thePP 93 3% 213? ii i? 21 '22 Trace The test results reproduced in Table I1and the permeability 77.30 14. 05 4.40 2. s0 8. 77 0 values shown inFIGS. 4 to 7 as a function of temperature 3;: ,8 1%: g i: fig g: 2? 132Trace demonstrate that the magnetic alloys with nickel-iron base ob-72.20 14. 05 12. 30 g 1 g. 77 8 tamed according to th1s1nvent1on andwhen heat treated as set $1 $8 Z3 1;: 0 35 forth herein have in therange of low temperatures a far higher 70.75 14.10 13. 00 0.72 3.8 8-8:initial permeability than the presently available high grade 3: Q3 1 0commercial nickel-iron materials whose maximum permea- 70. 15 17.15 03.05 g. 78 g a bility is in the range of room temperature as it is shownby the (0. 05 16. 25 0 4. 1 7 race dotted curvg infiFlGi TABLE 11 Finalheat treatment Test Tem- Maximum temperainitial pera- Permeability 0.5mile. at- Alloy Time ture permeability ture Shape of permeability, No.(hrs) C.) at, 0.5 1110c. C.) 200 C. 196 C. 0. temperature curve 2 60054,000 260 54,000 44,000 20,000 Maximum below 260 c. 2 2 30,000 52,000Narrow maximum.

2 60,000 32,000 Broad maximum. 3 2 63,000 34,000 (Fig. 4) 2 00, 000 23,000 Do. 4 2 44, 000 26, 000 Narrow maximum.

2 69,000 32,000 Broad maximum. 5 2 04,000 32,000 Do. 2 00, 000 27,000Do. 6 2 46,000 25,000 Maximum below 269 c. 2 27,000 17,000 7 2 80,00043,000 Broad maximum.

2 68,000 24,000 D0. 8 2 03,000 25,000 Fi 5). 2 53,000 Do. 0 2 15,00032,000 Fi 5). 10 2 100,000 27, 000

2 52,000 18,000 ll 2 16,000 10,000 Very narrow maximum. 12 2 52,00032,000

2 33,000 20,000 Maximum under -250 2 54, 000 17, 000 14 2 30,000 20,0002 32,000 14,000 15 2 30,000 25,000 (Fig. 7)- 2 70, 000 Do. 10 2 12, 00010,000

2 43,000 36,000 Very narrow maximum. 17 2 3,000 17,000 (Fig. 0) 2 14,00080,000 Do. 18 2 43,000 22,000 Maximum under 260 c. 13 2 00,000 14,000(Fig. 0). 2 30,000 Do. 20 2 50,000 32,000 Broad maximum.

From the test data in Table II and from the permeabilitytemperaturecurves in FIGS. 4 to 9 it can be seen how the position and the form ofthe maxima of permeability depend on the composition of the alloys andon the heat treatments. As a principle for selection of a suitablematerial with easy magnetization at low temperatures it was found thatin general the maximum of permeability is shifted toward the lowtemperatures by a lower final heat treatment temperature and also bylonger annealing times. To avoid the Perminvar effect the final heattreatment must be at a temperature above the Curie temperature.

Another relationship found to exist in the alloy of the presentinvention is that where the molybdenum content increases toward theupper limit at any given nickel level the final heat treatmenttemperature must decrease toward the Curie temperature in order toachieve the high initial permeability. Also, where the alloy has acomposition near the line F-G of FIG. 1 increasing nickel contentsrequire higher final heat treatment temperatures approaching 550 C. inorder to obtain the high initial permeability at low temperatures.

The maximum initial permeability of the alloys found outside of therange limit A B C D E A (Nos. 9, 11, 16 and 17) cannot be shifted intothe temperature range of liquid nitrogen and of liquid helium by a finalheat treatment at a lower temperature.

The advantage obtained with the invention consists in making available amore ductile magnetically soft material which has a very highpermeability at the low temperatures, especially in the range betweenl80 and 269 C. The relationships which have been found permit theselection of the alloy and the final heat treatment so that the highestpossible permeability or a permeability of predetermined value in agiven range may be selected at will.

The magnetic materials according to this invention with the nickel-ironbase with high permeability at low temperatures are suitable above allfor the low temperature cooled magnetic shields, current transformers,and transmitters as well as for relays, magnetic switches, memories, andmultipliers.

I claim as my invention:

l. A heat treated ductile nickel-iron base magnetic alloy consistingessentially of, by weight, from about 8.9% to about 27.6% iron, up toabout 12.5% copper, up to about 4.6% molybdenum, from about 0.2% toabout 1.0% manganese and the balance essentially nickel, the alloyexhibiting maximum initial permeability at subzero temperatures when thealloying components within the ranges set forth hereinbefore arebalanced to provide an alloy having a composition within the area ABCDEAof FIG. 1 and in which the copper content is balanced with respect tothe remainder of the alloying components to provide an alloy having thecomposition falling within the area KQLMNSOPK of FIG. 2, and the alloyhas been given a final heat treatment at a temperature within the rangebetween the Curie temperature and 5 50 C.

2. The alloy of claim 1 in which the copper content is balanced withrespect to the remainder of the alloying component to provide an alloyhaving the composition within the area QRSTQ of FIG. 2.

3. The alloy of claim 1 in which the alloying components are balanced toprovide an alloy having the composition within the area FGHJF of FIG. 1.

4. A readily workable heat treated nickel-iron base alloy containingcopper, molybdenum and manganese, the alloying components being selectedto provide an alloy having a composition falling within the area FGHJFof FIG. 1, the copper content is selected with respect to the remainingelements to provide a composition within the area QRSTQ of FIG. 2 andthe alloy has been given a final heat treatment at a temperature withinthe range between the Curie temperature and 5 50 C, said alloy beingcharacterized by exhibiting its maximum initial permeability at atemperature of below about l 00 C.

5. A magnetic core suitable for use at temperatures below about l00 C.having a high initial permeability and formed from the alloy of claim 1.

6. A heat treated ductile nickel-iron base magnetic alloy consistingessentially of, by weight, from 8.9 to 27.6% iron, up to 12.5% copper,up to 9.6% molybdenum, from 0.2% to 1.0% manganese and the balancenickel with incidental impurities, the alloy exhibiting maximum initialpermeability at a temperature below I 00 C. when the alloying componentswithin the ranges set forth hereinbefore are balanced to provide analloy havin a composition withinthe area FGHJF of FIG. 1 and in whrc thecopper content s balanced with respect to the remainder of the alloyingcomponents to provide an alloy having the composition falling within thearea KQLMNSOPK of FIG. 2 and the alloy has been given a final heattreatment at a temperature within the range between about 440 C. andabout 550 C.

2. The alloy of claim 1 in which the copper content is balanced withrespect to the remainder of the alloying component to provide an alloyhaving the composition within the area QRSTQ of FIG.
 2. 3. The alloy ofclaim 1 in which the alloying components are balanced to provide analloy having the composition within the area FGHJF of FIG.
 1. 4. Areadily workable heat treated nickel-iron base alloy containing copper,molybdenum and manganese, the alloying components being selected toprovide an alloy having a composition falling within the area FGHJF ofFIG. 1, the copper content is selected with respect to the remainingelements to provide a composition within the area QRSTQ of FIG. 2 andthe alloy has been given a final heat treatment at a temperature withinthe range between the Curie temperature and 550* C, said alloy beingcharacterized by exhibiting its maximum initial permeability at atemperature of below about -100* C.
 5. A magnetic core suitable for useat temperatures below about -100* C. having a high initial permeabilityand formed from the alloy of claim
 1. 6. A heat treated ductilenickel-iron base magnetic alloy consisting essentially of, by weight,from 8.9 to 27.6% iron, up to 12.5% copper, up to 9.6% molybdenum, from0.2% to 1.0% manganese and the balance nickel with incidentalimpurities, the alloy exhibiting maximum initial permeability at atemperature below -100* C. when the alloying components within theranges set forth hereinbefore are balanced to provide an alloy having acomposition within the area FGHJF of FIG. 1 and in which the coppercontent is balanced with respect to the remainder of the alloyingcomponents to provide an alloy having the composition falling within thearea KQLMNSOPK of FIG. 2 and the alloy has been given a final heattreatment at a temperature within the range between about 440* C. andabout 550* C.